Sen. Marco Rubio of Florida has for months been single-handedly holding up the nomination of William Thomas, an openly gay African American Miami judge, to a federal district court.

Rubio’s indefinite hold on Thomas’ nomination is one of the most egregious examples yet of Senate Republicans using the obscure “blue slip” procedure to prevent home-state judicial nominees from even having a hearing before the Senate Judiciary Committee.

Under a Senate custom that has varied over time Judiciary Committee Chairman Patrick Leahy will not advance a nominees’ consideration -- won’t even hold a hearing, let alone take a vote -- until both of that nominee’s home-state senators return a “blue slip” giving their permission for a nomination to go forward. The blue slip doesn’t indicate a senator’s approval of the nominee – the senator is still free to vote against the nominee and to lobby their fellow senators to do the same. It just means that the nominee can be considered by the Judiciary Committee and then the full Senate. But if just one senator doesn’t return a blue slip, the nomination won’t see the light of day.

Republican senators have been routinely using this tactic of withholding blue slips in order to slow-walk President Obama’s judicial nominees. Currently, five nominees are being held back because one or both senators have refused to return blue slips. And all are women or people of color.

Because the blue slip process is secretive and little-known, senators are often able to get away with holding nominees this way with little public pressure and no public explanation.

Rubio, however, faced pressure from the Florida legal community in recent weeks for his failure to return blue slips for Thomas and another Florida nominee, Brian Davis. The senator finally gave in under pressure and allowed Davis’ nomination to go forward, but is digging in his heels on his blockade of Thomas.

Rubio’s stated reasons for blocking Thomas’ nomination are exceptionally flimsy. He has cited two cases where he claims Thomas gave insufficiently harsh sentences in criminal trials; in one case, even the prosecutor has defended Thomas’ judgment and a local judge has written to Rubio to correct the record. In the other case the senator cites, Judge Thomas sentenced the defendant to death, which Rubio seems to think was insufficiently harsh. It is clear that there is no merit to the senator’s claims. Holding hearings on this nominee would help clarify that, if they were allowed to take place.